1. Field of the Invention
The invention relates to a method for the manufacture of pipes of thermo-plastics with transverse profile features, comprising mold segment halves which are circulated and, subsequent to an injection head, disposed in two lines opposite to each other, with the mold segment halves of a line not being interconnected, and which complement one another by twos along a straight molding path, forming a closed hollow mold; wherein each of the mold segment halves of a line is guided out of the molding path at the downstream end thereof and substantially at right angles to a direction of production by means of a conveying device and is re-circulated to the up-stream end of the molding path, where it is again inserted in the molding path and attached to the respective mold segment half that leads in the direction of production; wherein downstream of the downstream end of the molding path and on both sides thereof, an additional first mold segment half is kept in a first parking position for insertion in the molding path; the invention further relates to an apparatus for putting the method into practice.
2. Background Art
A method of the generic type and an apparatus of the generic type are known for example from U.S. Pat. No. 5,693,347.
In order to obtain a reliable connection of pipes that are provided with a socket at one end and with a spigot at the other end, a minimum length of the connecting socket is required. Practice and literature proceed from a so-called plug-in length i.e., a length by which the spigot is inserted into the socket. As a rule, the plug-in length must exceed the outside pipe diameter by 30 percent. If pipes of very great diameters are to be manufactured, this means that, given a single-piece design of the mold segment halves that serve for molding the socket, these mold segment halves and consequently all the mold segment halves will be very long, which is accompanied with some problems in terms of manufacturing. In particular, the mold segment halves will become very heavy, demanding for an enormous increase in the power required in the process, in particular the accelerating power. This applies especially to cases when the socket and spigot are molded directly one after the other during the continuous manufacture of the pipe, with an intermediate section being in between which has to be cut out subsequently.
When the apparatus is embodied in the way of a gantry crane, having a conveying carriage and conveying arms, as known from U.S. Pat. No. 5,693,347, the entire system is largely free from torque i.e., there are no tilting forces that have to be compensated by corresponding constructional measures. This known apparatus is applicable in particular where pipes of great diameters are to be produced, requiring very big and heavy mold segment halves.
EP 0 636 462 B1, U.S. DES. Pat. No. 199 46 571 C2 and U.S. DES. Pat. No. 200 11 668 U1 teach further apparatuses in which mold segment halves that serve for molding sockets can be added to, and removed from, the circulating mold segment halves. In all these cases—as with the apparatus of the generic type—it is only possible to mold a pipe section that deviates from a standard pipe, for instance a socket that can be molded by means of a pair of mold segment halves.